The asynchronous transfer mode (ATM) technology is a flexible form of transmission which allows any type of service traffic, voice, video or data, to be multiplexed together onto a common means of transmission. In order for this to be realised, the service traffic must first be adapted typically into 53 byte cells comprising 5 byte headers and 48 byte payloads such that the original traffic can be reconstituted at the far end of the ATM network. This form of adaptation is performed in the ATM adaptation layer (AAL).
An ATM exchange may support POTS or ISDN services as well as B-ISDN services. In an ATM exchange with 2 Mb/s trunk circuits with independent calls on each 64 kb/s channel it is desirable that traffic once adapted to ATM should remain in ATM up to the destination narrow band port. It is further desirable that a physical trunk at e.g. 155 Mb/s should be able to carry logical routes to more than one destination as 155 Mb/s is generally considered to be too large a capacity for trunking within a narrow band service network. If the logical routes are of n.times.64 kb/s where n.gtoreq.6 then the cell assembly delay is reduced to the point that echo cancellation is no longer necessary. The cell assembly delay of a single 64 kb/s circuit is 6 msec which requires echo cancellation for interworking with the existing narrow band network.
It has been observed that the traffic demand on routes between narrow band exchanges varies widely during the business day. There is typically a busy hour at the start of the working day and a second busy hour following lunch which is usually at a somewhat lower demand level. Nominal peak capacity of a route also varies significantly throughout the year. Routes in residential districts may have different peak periods but are also dynamically variable to a similar degree. The need to avoid this congestion can require an uneconomic provision of resources to ensure that demand peaks can be met. In an approach to this problem it has been proposed that the capacity of the paths that are used to support traffic from specific services may be varied dynamically according to service demand, e.g. time of day. Such a technique is described in specification No. EP-A2-0635958 and in U.S. Pat. No. 5,271,005.
It is an object of the invention to provide an improved system and method for controlling the capacity of a virtual trunk group on a call-by-call basis.